Tamper resistant receptacles are known in the art. “Tamper Resistant” or “TR” receptacles are a class of electrical receptacle outlets configured to deny access to the device's electrical contacts unless force is applied simultaneously to both the hot and neutral plug openings of the device pursuant to NEC Code 406.11 et seq. The Code and related regulatory requirements provide that not only must the outlet openings remain blocked unless force is applied to both openings at the same time, but also that any foreign object 1/32 inch or larger, must be prevented from bypassing the blocking member of a plug opening.
As will be appreciated, these requirements were enacted in response to the phenomena of small children curiously inserting a small toy or metal object into the hot or neutral opening of a receptacle and suffering electrical shock, burns, or even death.
In meeting the standard and providing the level of protection sought from these devices, the art has gravitated towards a configuration of receptacles utilizing cooperating shutter members to block access beyond the faceplate openings of the outlet. Specifically, to ensure that force directed into only one of the two blade openings is prevented from reaching the electrical contact that lies beneath, a sliding shutter mechanism is spring-biased into a position blocking (or “shuttering”) the blade opening from underneath the faceplate. The shutter physically prevents an object entering the blade opening from reaching the electrical contact below that shutter. In order to allow the shutter of a respective blade opening to be uncovered, the spring-bias must be overcome by a camming action caused by the other plug blade during insertion in the other blade opening.
To this end, the most common prior art configuration of a TR receptacle includes a shutter assembly comprising a pair of cooperating shutters. Each of the shutters includes a blocking portion positioned below a respective one of the blade openings blocking access to the contacts. Each of the shutters also includes a cam portion that extends to the opposite blade opening that receives contact from a plug blade and translates the vertical force of a plug blade and camming action into a lateral sliding displacement of the blocking portion. Thus, force by vertical insertion of a plug-blade on the neutral blade opening will move the shutter from obstructing access to the electrical contact below the hot blade opening, and vice versa. Specifically, for example, during insertion of a plug, the neutral blade tine will cam against and past the shutter cam surface forcing the shutter cam arm to move laterally, thereby overcoming the spring bias of the shutter and causing the hot blade shutter blocking portion to slide into a position away from and revealing the electrical contact beneath the hot blade opening. Likewise, force on the hot blade opening will contact the cam surface and allow the blade to cam past and move the arm and compress the spring to move the shutter blocking portion that covers the neutral blade opening out of the way. As will be appreciated, with this configuration, when a child tries to insert a toy into either opening of the outlet, the blocking portion of the shutter remains immobile from the spring bias of the opposite shutter and prevents the child from reaching the electrical contact. However, when both blades of an electrical plug contact the shutters simultaneously, the simultaneous force and camming action allows both blades to continue their downward insertion by simultaneously sliding respective shutter blocking portions laterally out of the way of the electrical contacts of the opposite shutter until the blades cam past the shutters and are able to properly “plug in” to the outlet's internal face contacts.
Existing prior art TR receptacle designs and their operational details are available in U.S. Pat. No. 4,379,607 to Bowden, Jr.; U.S. Pat. No. 7,645,148 to Carbone et al.; U.S. Pat. No. 8,187,011 to Baldwin et al., and U.S. Publ. No. 2013/0295788 to Baldwin, et al. and the references cited therein, the entire contents of which are hereby incorporated by reference in their entirety.
The cam surface of most prior art devices is an inclined “ramp” of about 45° that is of a length sufficient to cause lateral displacement during insertion of a distance that is equal to the distance necessary to un-shutter a horizontal blade opening (typically about 1.8 mm). One drawback with these devices is that the ramp does not provide enough lateral movement to be effective for 20 A receptacles that have a perpendicular blade opening for the 20 A neutral plug blade. To be effective with a 20 A device, a much larger amount of lateral movement is required. The height of the receptacle logistically eliminates the ability to use a longer ramp to provide the necessary clearance. Another drawback with some prior art devices is that the respective shutters are spring-biased towards one another, meaning that additional insertion force may be necessary to overcome the friction caused by the shutters sliding over one another in opposite directions.
The foregoing underscores some of the problems associated with conventional TR receptacles. Furthermore, the foregoing highlights the long-felt, yet unresolved need in the art for a TR receptacle with cooperating shutters that is effective in 20 A receptacles having a perpendicular neutral blade receiving slot. Moreover, the forgoing highlights the long-felt, yet unresolved need in the art for a TR receptacle design that may be modified to accommodate a 20 A neutral blade at a reasonable cost.